I keep reading it is 2304 bytes.

Wikipedia states it is 7981 bytes.

On my WiFi AP, I can set the RTS threshold with a value of 0-2346 bytes (I guess it's MTU + the MAC/PHY header ?)

Where does this 7981 bytes come from, and can we have a definite answer on the 802.11 MTU size ? Is it 2304 bytes ?

If MTU = 2304 bytes, what is the total frame size of a WPA2 packet (assuming the MTU is fully saturated) ?

  • Sometimes, you get what you pay for with Wikipedia. If you look at the wiki for 802.11, it says, "The payload or frame body field is variable in size, from 0 to 2304 bytes plus any overhead from security encapsulation, and contains information from higher layers.". – Ron Maupin Jul 9 '16 at 14:13
  • And the RTS threshold isn't the MTU -- it's the size where CTS/RTS handshaking happens. – Ricky Beam Jul 9 '16 at 20:06
  • Are you asking what is the recommended MTU or the theoretical max? Recommended by most vendors = 1500 byte. – AJ. Nov 29 '16 at 5:44

Here is the answer : I couldn't find this value of 7981 bytes anywhere, and the links on wikipedia were dead, so I edited it to 2304.

The maximum 802.11 MTU is 2304 bytes.

Here are the different possible maximum frame size of a 802.11 packet, according to the encryption scheme in use :

MTU + MAC Header + Encryption Header

  • WEP : 2304 + 34 + 8 = 2346 bytes
  • WPA (TKIP) : 2304 + 34 + 20 = 2358 bytes
  • WPA2 (CCMP) : 2304 + 34 + 16 = 2354 bytes

If QoS is used, an additional 2 bytes header is added before the payload, increasing the frame size by 2 bytes.

802.11 MPDU

Note that the Encryption header is missing on the picture. It would be placed after QoS Control, inside the frame body, but would not decrease the available 2304 bytes for application data.

In addition, the "Address 4" field of a 802.11 frame is often not used, effectively reducing the frame size by 6 bytes for most 802.11 MPDU.

  • 1
    Please note that an MTU of that size cannot be bridged to a wired ethernet network where the MTU is 1500 bytes. – Ron Maupin Dec 14 '16 at 23:31

I suppose that the answer regarding mentioned "7981 bytes" is in the specs.

IEEE Standard for Information technology— Telecommunications and information exchange between systems Local and metropolitan area networks— Specific requirements, Part 11: Wireless LAN Medium Access Control(MAC) and Physical Layer (PHY) Specifications, p.381

The Frame Body field is of variable size. The maximum frame body size is determined by the maximum MSDU size (2304 octets), plus the length of the Mesh Control field (6, 12, or 18 octets) if present, the maximum unencrypted MMPDU size excluding the MAC header and FCS (2304 octets) or the maximum A-MSDU size (3839 or 7935 octets, depending upon the STA’s capability), plus any overhead from security encapsulation.

  • You're right, it probably had to do with this. Regardless, A-MSDU is frame aggregation, so although there's only one set of headers for multiple frames, that's not what I was really looking for back when I created this question. – pHeoz Feb 20 at 11:38
  • @pHeoz I agree, it's not the actual answer to your initial question, but i believe that it clarifies some part of it and gives a lead on where to look for the answers at the first place. – diabolusss Feb 21 at 12:21

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